The present invention relates generally to a fluid control valve and, more particularly, to a variable force solenoid control valve with reduced size and with reduced mechanical and magnetic hysteresis.
Solenoids are well known in a variety of industries and are utilized for a variety of applications. On such industry that utilizes solenoids, is the automotive industry. One of the many applications within the automotive industry where solenoids are utilized is in automatic transmission systems. Often vehicles utilize an automatic transmission controller that uses solenoids to control the pressure of the transmission fluid. The control of transmission fluid pressure can be used to engage and disengage the transmission clutch in response to an electrical input signal supplied to the solenoid, or the control of transmission fluid pressure can be used to simply maintain transmission line pressure.
One particular type of solenoid is commonly referred to as a variable force solenoid control valve. Typically, variable force solenoid control valves are provided with fluid control components consisting of a spool valve having a stem and two radially extending lobes or lands. The spool valve is movably confined within a valve body to create flow restrictions for pressure regulation. Fluid passages are provided in the valve body which communicate with the various surfaces of the spool valve. Commonly, fluid at inlet pressure is delivered to a flow restriction provided between the two spool valve lands. The flow restriction enables the fluid pressure to be reduced to a desired outlet control pressure.
Although the variable force solenoid control valves known in the prior art have generally been successful in meeting the demands of the industry, these control valves can be further improved upon. Improvements in the areas of cost, size, reduction of hysterisis, sensitivity, and calibration are still possible and highly desirable. Even recent developments in solenoid design, such as the use of a flux shunt, leave significant room for improvement. The ever present need for reductions of cost and weight combined with the need for increased efficiency, are often driving factors in the automotive industry (as well as elsewhere).
It would therefore be highly desirable to have a variable force solenoid control valve that made further progress towards reductions in cost, weight and hysteresis and additionally made improvements to control sensitivity and calibration.
It is therefore an object of the present invention to provide a variable force solenoid control valve that provides reductions in cost, weight, and hysteresis. It is a further object of the present invention to provide a variable force solenoid control valve that provides improvements to control sensitivity and calibration.
In accordance with the objects of the present invention, a variable force solenoid control valve is disclosed that includes an electromagnetic coil positioned within a housing and a spool valve positioned within a central bore of a valve body. An armature is axially positioned within the coil, and includes a pin element and a check ball. An armature spring biases the armature, and thereby the check ball, against an opening in the central bore when the coil is not energized. An upper pin bearing and a lower pin bearing limit the armature to coaxial movement within the housing. The spool valve includes an internal chamber and a pair of sealing lands that selectively seal a supply port and a control port within the valve body. A pole piece, including an annular flux shunt portion, is threadably engaged with the housing to control a working air gap between the pole piece and the armature. The flux shut portion more radially directs the electromagnetic field lines to weaken the magnetic force as the armature moves closer to the pole piece. A flux tube is positioned within the housing.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.